One of the hallmarks of a mature discipline is its ability to make predictions that can be used to test scientific theories. Scientific predictions do not necessarily have to be con­cerned with future events; they can be made about what occurred in the past. I illustrate such retrospective prediction with a case study of conversion to Christianity in the Ro­man Empire. The bulk of the paper deals with the logic and methodology of setting up a scientific prediction in macrosociology. The specific case study I develop is the possible state collapse in Saudi Arabia. The theoretical setting is provided by the demographic-structural theory of state collapse. The starting point is a previously developed model for political cycles in agrarian societies with nomadic elites, loosely based on the ideas of Ibn Khaldun. I modify the model to fit the characteristics of the modern Saudi Ara­bian state and estimate its parameters using data from published sources. The model predicts that the sovereign debt of Saudi Arabia will eventually reach unmanageable proportions; the fiscal collapse will be followed by a state collapse in short order. The timing of the collapse is affected by exogenous events (primarily, fluctuations in world oil prices) and by parameter uncertainty (certain parameters of the model can be estimated only very approximately). The generalized prediction of even­tual Saudi collapse together with subsidiary relationships specifying how variations in exogenous factors and parameters affect the future trajectory is the "Ibn Khaldun sce­nario." A major theoretical alternative is provided by a set of ideas and specific recom­mendations suggesting how Saudi Arabia can avoid crisis by reforming its economy and liberalizing its political system (the "IMF scenario"). The main purpose of the proposed test, therefore, is to determine which of the two theoretical scenarios will best describe the trajectory of the Saudi state over the next decades.